Effect of cooling and coating on thermoplastic starch/poly(lactic acid) blend sheets

The influence of the processing conditions (cooling rate) and coating on the physicochemical properties of thermoplastic starch/poly(lactic acid) blend sheets was studied. Two cooling rates were used: fast and slow, and in the latter case the sheets were both non-coated and coated with cross-linked chitosan. The physicochemical properties investigated were crystallinity, morphology, water affinity (moisture sorption isotherm, water vapor permeability, water solubility and contact angle) and mechanical properties. In general, the sheets cooled at the slow rate were more crystalline, less permeable and less soluble in water than those cooled at the fast rate. They also produced a more homogeneous morphology. The coated sheets were less soluble in water and mechanically stronger than uncoated sheets cooled at the slow rate. The concentration of plasticizer in the TPS affected only the sorption isotherm and contact angle since a higher plasticizer content caused a greater affinity for water.